/Engine/Source/Runtime/ApplicationCore/Public/GenericPlatform/GenericPlatformInputDeviceMapper.h
Remap the legacy platform LocalUserIndex (often the same as ControllerId) to aFPlatformUserId. This is useful in cases where the input device id is not needed.
A platform-allocated user id, or PLATFORMUSERID_NONE
[FPlatformUserId](API\Runtime\Core\Misc\FPlatformUserId) GetPlatformUserForUserIndex ( int32 LocalUserIndex )